CN112262614B

CN112262614B - Method for controlling a cooking zone of an induction cooking hob

Info

Publication number: CN112262614B
Application number: CN201980039291.6A
Authority: CN
Inventors: 弗雷德里科·巴莱斯特; 劳伦特·让纳托; 亚历克斯·维罗利; 马西莫·诺斯特罗
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2018-06-16
Filing date: 2019-06-03
Publication date: 2023-09-22
Anticipated expiration: 2039-06-03
Also published as: CN112262614A; BR112020025536A2; AU2019284795A1; EP3808155A1; AU2019284795B2; US11825585B2; EP3582586A1; US20210212176A1; EP3582586B1; WO2019238447A1

Abstract

The invention relates to a method for controlling a cooking zone (16) of an induction cooking hob, wherein said cooking zone (16) comprises at least one induction coil (16) and is supplied by a generator (14) comprising a power switch. The method is performed by: the power switch is controlled by a gate drive signal (18) comprising a deactivation pulse length (Toff) and an activation pulse length (Ton). The switching period (T) of the gate drive signal (18) is given by the sum of the activation pulse length (Ton) and the deactivation pulse length (Toff). The driving frequency (f) of the power switch is the inverse of the switching period (T). The deactivation pulse length (Toff) is dependent on the resistance (28) and inductance (30) of the induction coil (16). The activation pulse length (Ton) varies in accordance with the requested power of the cooking zone (16). A series of constant activation pulse lengths (Ton) are activated to determine the optimal deactivation pulse length (Toff).

Description

Method for controlling a cooking zone of an induction cooking hob

The present invention relates to a method for controlling a cooking zone of an induction cooking hob. Further, the invention relates to an induction cooking hob.

In the cooking zone of an induction cooking hob acoustic noise may occur due to frequency jitter. Such frequency dithering is an undesirable and unavoidable effect in oscillator circuits.

WO 2013/064331 A1 discloses an induction heating cooker. The power switch is controlled by a gate drive signal comprising a conduction time Ton and a non-conduction time Toff. The on-time Ton depends on the power level adjustment performed by the user. The non-conduction time Toff depends on the resistance and inductance of the induction coil. The comparator compares the output voltage of the rectifier with the resonant voltage at the collector node of the power switch in order to detect the presence and characteristic features of the cooking vessel and to determine and update the non-conduction time Toff of the power switch.

EP 2999304 A1 discloses a method for operating an induction cooking hob. The alternating current flowing through the induction coil is activated by an enable signal having a variable pulse duration. When the heating process is started, the duration of the enable signal pulse is shortened to reduce acoustic noise.

EP 2999304 A1 discloses an induction cooking hob, wherein the power switch is controlled by a signal comprising pulses. The power is adjusted by the duration of the pulse. The reduction of the pulse duration reduces acoustic noise due to high on-current.

It is an object of the present invention to provide a method for controlling a cooking zone of an induction cooking hob, which reduces acoustic noise due to frequency jitter and determines an optimal deactivation pulse length with low complexity.

This object is achieved by a method according to the present disclosure.

According to the present invention, there is provided a method for controlling a cooking zone of an induction cooking hob, wherein said cooking zone comprises at least one induction coil and is supplied by a generator comprising a power switch, and wherein the method is performed by the steps of:

the power switch is controlled by a gate drive signal comprising a deactivation pulse length Toff and an activation pulse length Ton,

wherein the switching period T of the gate drive signal is given by the sum of the activation pulse length Ton and the deactivation pulse length Toff,

wherein the driving frequency f of the power switch is the inverse of said switching period T,

wherein the deactivation pulse length Toff depends on the resistance and inductance of the induction coil,

-wherein the activation pulse length Ton varies according to the requested power of the cooking zone, and

-wherein a series of constant activation pulse lengths Ton are activated to determine an optimal deactivation pulse length Toff.

The core of the invention is that: on the one hand it is assumed that the deactivation pulse length Toff is constant and that the activation pulse length Ton varies in dependence on the request power, and on the other hand the optimal deactivation pulse length Toff is determined by activating a series of constant activation pulse lengths Ton. The gate drive signal can be controlled by only changing the activation pulse length Ton. This reduces frequency jitter and the acoustic noise generated. Activating a series of constant activation pulse lengths Ton does not require any additional hardware. In practice, the optimal deactivation pulse length Toff is determined by multiple activations of the power switch.

Preferably, the deactivation pulse length Toff is constant for a particular combination of the induction coil and cooking vessel.

Further, the deactivation pulse length Toff may depend on the final resistance value and inductance value when the cooking vessel is placed on the cooking zone. The combination of a constant deactivation pulse length Toff and a variable activation pulse length Ton is a fundamental attribute of the invention.

In particular, the deactivation pulse length depends on the resistance, inductance and capacitance of the system formed by the induction coil and the cooking vessel.

In this case, the capacitance depends on the position of the cooking vessel above the induction coil.

Preferably, the deactivation pulse length Toff is detected after the generator has been activated.

The power switch is driven if the detected deactivation pulse length Toff is within a predefined range. Otherwise, the generator is stopped.

For example, the constant activation pulse length is activated five to twenty times, preferably ten to fifteen times.

Furthermore, the constant activation pulse length Ton may be between six microseconds and forty microseconds, preferably about eleven microseconds.

Further, the presence and/or position of the cooking vessel is detected.

Typically, the method is implemented in hardware, software, or a combination of hardware and software.

Furthermore, the present invention relates to an induction cooking hob, wherein said induction cooking hob is provided for the method of the present disclosure.

In particular, the induction cooking hob comprises at least one analog to digital converter. Preferably, the analog-to-digital converter is integrated within a microcontroller of the induction cooking hob.

The analog-to-digital converter may be provided for detecting the shape of the voltage and/or current of the power switch of the induction cooking hob.

Finally, the invention relates to a computer program product stored on a computer usable medium, the computer program product comprising computer readable program means for causing a computer to perform the above method.

The novel and inventive features of the present invention are set forth in the appended claims.

The invention will be described in further detail with reference to the accompanying drawings, in which:

figure 1 shows a schematic diagram of the electrical circuit of the cooking zone of an induction cooking hob according to a preferred embodiment of the present invention,

figure 2 shows a schematic time diagram of an automatic triggering pulse width modulation mode of a cooking zone of an induction cooking hob according to the prior art,

figure 3 shows a schematic equivalent circuit diagram of a cooking zone of an induction cooking hob with a cooking vessel,

figure 4 shows a schematic time diagram of a damped oscillation with several damping parameters,

figure 5 shows a schematic flow chart of an algorithm for evaluating pulse width and detecting a cooking vessel according to a preferred embodiment of the invention,

figure 6 shows a schematic time diagram of an example of an automatic triggering pulse width modulation mode of a cooking zone of an induction cooking hob according to a preferred embodiment of the present invention,

FIG. 7 shows a detailed time chart of the calculation of the length of the deactivation pulse and the detection of the presence of a cooking vessel in accordance with the present invention, and

fig. 8 shows a schematic time diagram of the activation of the free-running pulse width modulation mode of the induction coil of the induction cooking hob according to the present invention.

Fig. 1 shows a schematic diagram of a circuit of a cooking zone of an induction cooking hob according to a preferred embodiment of the present invention.

The circuit includes a user interface 10, a microcontroller 12, a generator 14, and an induction coil 16. Instead of the induction coils 16, the cooking zone may comprise two or more induction coils 16, wherein the induction coils 16 are supplied by the generator 14 at the same frequency.

The user interface 10 is operated by a user. In particular, the user selects the requested power for the induction coil 16. The microcontroller 12 controls the generator 14. The generator 14 supplies the induction coil 16 at a frequency corresponding to the requested power. In this example, the generator 14 is a quasi-resonant generator. The generator 14 comprises a power switch, e.g. an IGBT. The induction coil 16 provides an alternating magnetic field to generate eddy currents in ferromagnetic portions of a cooking appliance on the induction cooking hob, thereby heating the cooking appliance.

Preferably, the circuit comprises at least one analog-to-digital converter. For example, the analog-to-digital converter is integrated within the microcontroller 12.

Fig. 2 shows a schematic time diagram of an automatic triggering Pulse Width Modulation (PWM) mode of the induction coil 16 of the induction cooking hob.

The timing diagram shows the gate drive signal 18, the input trigger signal 20 and the Vce signal 22 for the power switch. Typically, the power switch is an IGBT.

The activation pulse length Ton of the gate drive signal 18 for the power switch is set. The activation pulse length Ton applies the deactivation pulse length Toff of the gate drive signal 18. The deactivation pulse length Toff is maintained until the input trigger signal 20 across the power switch does not drop below the correct switching threshold 23 defined for that component. Otherwise, the generator 14 may be damaged or affected by significant power loss, which shortens the lifetime of the generator 14. In the prior art, the switch is triggered via hardware feedback by a defined threshold 23, wherein the method is referred to as an auto-triggering Pulse Width Modulation (PWM) mode.

The auto-triggering pwm mode allows the generator 14 and the power switch to be driven in the correct manner. However, auto-triggering pwm modes are affected by acoustic noise due to frequency jitter, high electrical noise sensitivity, and/or power variations over the power supply period. A trigger event 24 occurs when the Vce signal 22 crosses a threshold of about zero volts in the falling phase, which is below the threshold 23. The trigger event 24 changes the state of the input trigger signal 20 from low to high.

Fig. 3 shows a schematic equivalent circuit of the induction coil 16 and a cooking vessel on an induction cooking hob.

The equivalent circuit diagram of the induction coil 16 and the cooking vessel includes a resistor 28, an inductor 30 and a capacitor 32. Resistor 28 and inductor 30 are switched in series. A capacitor 32 is switched in parallel with the series resistor 28 and inductor 30. Resistor 28 and inductor 30 are properties of induction coil 16. Resistor 28 and inductor 30 are formed from coil windings and are then modified by the coupling of induction coil 16 to the cooking vessel. The capacitor 32 is formed by a separate physical component, has a constant value and is independent of the coil windings.

Fig. 4 shows a schematic time diagram of damped oscillations with several damping coefficients d. In this example, a time chart of damping coefficients d=0.4, d=0.6, d=0.8, d=1.0, d=1.5, d=2.0, and d=3.0 is shown. If the damping coefficient is d=0, the oscillation is undamped; if the damping coefficient is d <1, the oscillation is under damped; if the damping coefficient is d=1, the oscillation is critical; and if the damping coefficient is d >1, the oscillation is overdamped. In this case, the damping coefficient d is about 0.005, so the system is underdamped.

The damped oscillation model is applicable to quasi-resonant generators. When the power switch is in the on state, the Vce signal 22 is approximately zero volts; and when the power switch is in an off state, the Vce signal 22 has an underdamped response. Vce signal 22 has ringing at a frequency derived from the pulsing of ω x d and has a fixed level of potential difference Vdc, where ω is the frequency. The potential difference Vdc is a level between two limit points of the RLC circuit shown in fig. 3. In this case, the damping coefficient d is about 0.005, wherein the curve is similar to d=0.4 in fig. 4, but has a higher amplitude. The first zero crossing occurs after the first oscillation.

The level becomes the steady state condition final value, which is the main difference from the model in fig. 4. The decay rate of the observed signal is determined by the decay α given by:

α＝R/(2*L)＝ω*d，

where R is the resistance and L is the inductance of the induction coil 16, and the damping coefficient d describes the envelope of the oscillation.

The deactivation pulse length Toff is defined as the time required to respond to the minimum level being reached in the first oscillation period, while the activation pulse length Ton is the time to control the power switch in the on state and to keep the Vce signal 22 at zero.

The power switch may operate normally according to a switching period T given by:

T＝Ton+Toff，

and the driving frequency f is given by:

f＝1/T。

the driving frequency f is applied by the switching period t=ton+toff according to the power request. In contrast, the frequency ω mentioned above is related to the free oscillation of the system. Thus, the drive frequency f and the frequency ω differ due to the phase during the deactivation pulse length Toff, wherein Vdc is forced to zero.

Assuming that the deactivation pulse length Toff is a constant characteristic of the system, the power delivered by the generator 14 to the cooking vessel depends only on the current through the induction coil 16 and thus on the activation pulse length Ton.

The activation pulse length Ton is varied according to the desired target power, as is evident by the variation of the switching period P and the driving frequency f, since the deactivation pulse length Toff is constant for the coupling of the induction coil 16 to the cooking vessel.

Thus, the power can be controlled by the driving frequency f using only the activation pulse length Ton as a variable, whereas the deactivation pulse length Toff is set if the generator is in an on-state and the result is within a predefined range provided for driving the power switch as expected. If the operating conditions (e.g., coupling between the induction coil 16 and the cooking vessel) change during normal operation, the generator 14 is stopped and the measurements are repeated.

Fig. 5 shows a schematic flow chart of an algorithm for evaluating the deactivation pulse length Toff and detecting a cooking vessel in accordance with a preferred embodiment of the present invention.

The switching period depends on the hardware characteristics. One suitable method for obtaining a correct assessment of the deactivation pulse length Toff is an automatic triggering Pulse Width Modulation (PWM) mode, depending on the selected operating conditions. In particular, the auto-triggering PWM mode will be activated for a short interval during which a series of numbered switching pulses will be generated. The time distance between each feedback (the time distance set by the dedicated hardware properly designed for the function) is saved in a plurality of records. These data are elaborated to calculate the deactivation pulse length Toff, wherein the activation pulse length Ton selected for measuring the average period Tave is the minimum allowed by the invoked system.

When the method has started, the power is checked in step 34. If the power is zero, step 34 checks the condition. If the condition in step 34 is met, i.e. the power is zero, the generator 14 and the power control is stopped in step 36. If the condition in step 34 is not met, i.e. the power is not zero, the evaluation of the deactivation pulse length Toff is started in step 38. Then, the auto-trigger hardware circuit is enabled and a fixed activation pulse length Ton is set in step 40. Thereafter, a first pulse for driving the power switch is transmitted in step 42. The auto-trigger signal period is then measured in step 44.

In step 46 it is checked whether the measured value in step 44 has reached the target number. If the condition of step 46 is not met, the measurement of the auto-trigger signal period in step 44 is repeated. If the condition of step 46 is met, the automatic triggering circuit is disabled and the activation pulse length Ton is reset in step 48.

Then, it is checked in step 50 whether the minimum measurement number is within this range. If the condition in step 50 is not met, the time warp is activated in step 52 and the method returns again to step 42, wherein a first pulse for driving the power switch is transmitted. If the condition in step 50 is met, the presence of a cooking vessel is checked in step 54. It is necessary to detect the presence of the cooking vessel in order to ensure that the cooking vessel has been placed correctly on the area of the cooking zone.

If the condition of step 54 is not met (i.e. the cooking vessel is not present), then time warping is activated in step 52 and the method returns again to step 42, wherein a first pulse for driving the power switch is emitted. If the condition of step 54 is met (i.e., a cooking vessel is present), an average of the auto-triggering measurements is calculated in step 56. The deactivation pulse length Toff is then calculated in step 58. Thereafter, the deactivation pulse length Toff is applied and the minimum drive frequency and the maximum drive frequency are defined in step 60. Finally, the generator 14 is started and power in the free-running PWM mode is activated in step 62.

The free-running PWM mode starts with the following parameters:

Toff＝Tave-Min(Ton)，

f＝1/(Ton+Toff)，

wherein the active pulse length Ton for the free-running PWM mode is a controlled variable in order to meet the requested power acting on the drive frequency f.

Fig. 6 shows a schematic time diagram of an example of an automatic triggering Pulse Width Modulation (PWM) mode of the induction coil 16 of the induction cooking hob according to the present invention.

The timing diagram includes a gate drive signal 18, a Vce signal 22, and an auto-trigger feedback signal 64. The diagrams shown in fig. 2 and 6 relate to the same driving method. However, the diagram of fig. 2 is for power transfer, while the diagram of fig. 6 is for the management process of the deactivation pulse length Toff. In both cases, the Vce signal 22 crosses a threshold near zero volts, which triggers the state of the input trigger signal 20 to change from low to high upon a trigger event 24. After a delay 26 of 3 mus the gate drive signal 18 will be activated. The input trigger signal 20 in fig. 2 and the auto-trigger feedback signal 64 in fig. 6 are similar.

After the Vce signal 22 crosses the defined threshold 66, the auto-trigger feedback signal 64 rises regularly. The threshold 66 is different from the threshold 23 in fig. 2.

Then, the gate drive signal 18 rises after a fixed delay, and the power switch is activated. The delay ensures that the minimum level of the Vce signal 22 has been reached when the power switch is activated. In this example, the threshold 66 is 150V and the delay is 4 μs.

Fig. 7 shows a detailed time diagram of the calculation of the deactivation pulse length Toff and the detection of the presence of a cooking vessel according to the present invention.

The detailed time diagram shows the gate drive signal 18, the Vce signal 22, and the coil sample current 68. The activation pulse length Ton is 11 mus. At a drive frequency f of 30kHz, the average value was 34 mus. The target measurement number is ten.

Preferably, the activation pulse length Ton is constant. Typically, the activation pulse length Ton is between six and forty microseconds.

The deactivation pulse length Toff is given by:

Toff＝Tave-Min(Ton)＝34μs-11μs＝23μs，

and the driving frequency f is given by:

f＝1/(Ton+Toff)＝1/(20μs+23μs)

＝1/43μs＝23.3kHz

fig. 8 shows a schematic time diagram of the activation of the free running Pulse Width Modulation (PWM) mode of the induction coil 16 of the induction cooking hob according to the present invention. The time map is related to the parameters calculated above.

The timing diagram shows the gate drive signal 18, the Vce signal 22, and the auto-trigger feedback signal 64. Further, the time diagram shows a threshold 66. In this example, the trigger threshold 70 is 150V.

After the Vce signal 22 crosses the defined trigger threshold 70, the coil sampling current 68 rises regularly. However, the activation of the power switch is not synchronized with the trigger setting. The minimum level of the coil sampling current 68 is ensured by the reduction of acoustic noise due to frequency jitter, electrical noise immunity during power switch activation, and stability of power over the supply period.

Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the present invention as defined by the appended claims.

List of reference numerals

10 user interface

12 microcontroller

14 generator

16 cooking area, induction coil

18 gate drive signals

20 input trigger signal

22Vce signal

23 threshold value

24 trigger event

26 delay

Resistance of 28 induction coil

30 inductance of induction coil

32 inductance coil and capacitor of cooking vessel

34 step of checking Power

Step 36 of stopping the generator and power control

38 begin the step of evaluating the deactivation pulse length Toff

40 step of enabling the auto-trigger hardware Circuit and setting the fixed activation pulse Length Ton

42 step of transmitting a first pulse for driving the power switch

44 step of measuring the period of the automatic trigger signal

46 a step of checking whether the measurement in step 44 has reached the target number

48 disabling the automatic trigger circuit and resetting the step of activating the pulse length Ton

50 a step of checking whether the minimum measurement number is within the range

52 delay step

54 step of checking whether a cooking container is present

56 step of calculating an average of the auto-triggering period measurements

Step 58 of calculating the deactivation pulse Length Toff

60 apply deactivation pulse length Toff and define minimum drive frequency and maximum drive frequency

Step of rate

Step 62 starting the generator and activating the power in the free running PWM mode

64 automatic trigger feedback signal

66 threshold value

68 coil sampling current

70 trigger threshold

Ton activation pulse length

Toff deactivation pulse length

Tave average period

T switching period

f drive frequency

Omega frequency

Alpha attenuation

d damping coefficient

Resistance of R induction coil

Inductance of L-shaped induction coil

Claims

1. A method for controlling a cooking zone (16) of an induction cooking hob, wherein said cooking zone (16) comprises at least one induction coil (16) and is supplied by a generator (14) comprising a power switch, and wherein the method is performed by the steps of:

controlling the power switch by a gate drive signal (18) comprising a deactivation pulse length Toff and an activation pulse length Ton,

wherein the switching period (T) of the gate drive signal (18) is given by the sum of the activation pulse length Ton and the deactivation pulse length Toff,

wherein the deactivation pulse length Toff is dependent on the resistance (28) and the inductance (30) of the induction coil (16),

-wherein the activation pulse length Ton varies according to the requested power of the cooking zone (16), and

2. The method of claim 1, wherein the step of determining the position of the substrate comprises,

the deactivation pulse length Toff is constant for a particular combination of the induction coil (16) and cooking vessel.

3. A method according to claim 1 or 2, characterized in that,

when a cooking vessel is placed on the cooking zone (16), the deactivation pulse length Toff depends on the final resistance value and inductance value.

4. A method according to claim 1 or 2, characterized in that,

the deactivation pulse length Toff depends on the resistance (28), inductance (30) and capacitance (32) of the system formed by the induction coil (16) and cooking vessel.

5. The method of claim 4, wherein the step of determining the position of the first electrode is performed,

the capacitance (32) depends on the position of the cooking vessel above the induction coil (16).

6. A method according to claim 1 or 2, characterized in that,

the deactivation pulse length Toff is detected after the generator (14) has been activated.

7. The method of claim 6, wherein the step of providing the first layer comprises,

the power switch is driven if the detected deactivation pulse length Toff is within a predefined range, otherwise the generator (14) is stopped.

8. A method according to claim 1 or 2, characterized in that,

the constant activation pulse length Ton is activated five to twenty times.

9. The method of claim 8, wherein the step of determining the position of the first electrode is performed,

the constant activation pulse length Ton is activated ten to fifteen times.

10. A method according to claim 1 or 2, characterized in that,

the constant activation pulse length Ton is between six and forty microseconds.

11. The method of claim 10, wherein the step of determining the position of the first electrode is performed,

the constant active pulse length Ton is eleven microseconds.

12. A method according to claim 1 or 2, characterized in that,

the presence and/or position of the cooking vessel is detected.

13. A method according to claim 1 or 2, characterized in that,

the method is implemented in hardware, software, or a combination of hardware and software.

14. An induction cooking hob including at least one cooking area (16), characterized in that,

the induction cooking hob is provided for a method according to any one of the preceding claims 1 to 13.

15. The induction cooking hob according to claim 14, characterized in,

the induction cooking hob includes at least one analog to digital converter.

16. The induction cooking hob according to claim 15, characterized in,

the analog-to-digital converter is integrated within a microcontroller (12) of the induction cooking hob.

17. The induction cooking hob according to claim 15 or 16, characterized in,

an analog-to-digital converter is provided for detecting the shape of the voltage and/or current of the power switch of the induction cooking hob.

18. A computer usable medium having a computer program stored thereon, the computer program comprising computer readable program instructions for causing a computer to perform the method according to any of the preceding claims 1 to 13.